Onchocerciasis, or river blindness, is major filarial disease and is the fifth most common cause of blindness in the world. Limitations of control programs and the possible emergence of ivermectin resistant strains, suggest the need for alternative strategies for treatment and control of onchocerciasis. Currently, few suitable targets for chemotherapy have been precisely identified in filarial and other parasitic nematodes, due in part to a lack of understanding of the basic biology and biochemistry of these parasites. We propose to explore cysteine proteases as potential targets for chemotherapy. In our previous studies we identified a cysteine protease inhibitor, onchocystatin, and a cathepsin Z-like cysteine protease and proposed that they are essential for molting, growth and remodeling of the cuticle in larvae and adult worms, and the development of microfilariae. Recently, a cathepsin L-like enzyme and another member of the cystatin family were cloned, suggesting that the role of cysteine proteases and their endogenous inhibitors is more elaborate than initially thought. However, these proteins cannot be easily studied in O. volvulus in vivo as we lack a system for observing gene expression during the development of the parasite, particularly in its adult stages and in the gravid female worms. As many of the essential genes for nematode development are conserved in free living and parasitic nematodes, we will take advantage of the existence homologous proteins in C. elegans to understand the cellular processes by which the O. volvulus cysteine protease participate in the development of O. volvulus parasite in humans. This integrated approach of using genetic, molecular, biochemical and anatomical studies in this proposal, combined with a well defined organism will result in understanding how regulation of three distinct dysteine proteases is critical for the development and survival in C. elegans and O. volvulus. The proposed project has three specific objectives: 1. To establish the distinct physiological roles for each cathepsin Z and cathepsin L-like cysteine proteases and the two cystatin during C. elegans development, and then verify that the proposed O. volvulus homolugues will perform similar functions in O. volvulus. 2. To compare and contrast the developmental regulation and tissue specificity of O. volvulus and C. elegans cystatins. 3. To determine the substrate specificity of each O. volvulus and C. elegans cysteine protease and identify their specific inhibitors in vitro. We will determine the specific substrate specificity of the cysteine protease in vitro and determine which low molecular weight inhibitors could eventually be tested for their in vivo effect on adult worm survival and microfilariae development. This will provide the basis for developing effective drugs targeting cysteine protease to control onchocerciasis and filariasis in the future.